1. Field of the Invention
The present invention relates to a plasma treating method and an apparatus therefor and, more particularly to a plasma treating method suitable for simultaneously treating a plurality of samples under a vacuum by means of plasma and an apparatus therefor.
2. Description of the Prior Art
The so-called "batch type plasma treating apparatus", i.e., a plasma treating apparatus for ionizing a treating gas under a vacuum into plasma to simultaneously treat a plurality of samples by means of the plasma is disclosed in Japanese Patent Laid-Open No. 58-14939, for example. According to this disclosure, an opposed electrode and a sample electrode, on which the plural samples are placed in different positions, are mounted through a discharge space in a treating chamber so that those samples are simultaneously treated by means of the plasma which is generated under the vacuum between the opposed electrode and the sample electrode.
In the plasma treating apparatus disclosed above, those faces (hereafter referred to as "electrode faces") of the sample electrode, which are to be mounted with the samples, have an area 2.5 to 3 times as wide as the total area of the faces of the plural samples to be treated so that the ratio (hereafter referred to as an "area ratio") of the total area of the treated faces of the samples to the area of the electrode faces of the sample electrode takes a small value. During ionization of the treating gas, on the other hand, all the electrode faces of the sample electrode are used for discharge. From the discussions thus far made, electric power has to be supplied excessively according to the small area ratio to the sample electrode so as to generate plasma energy adequate for simultaneously treating the plural samples. As a result, there arises a problem that the capacity of power supply is undesirably large.
As is disclosed in Japanese Patent Laid-Open No. 59-64779, for example, on the other hand, there are placed an internal chamber which is equipped with upper electrode plates having gas exhaust ports such that it covers through a clearance at its lower end each of plural wafers placed on lower electrode plates held on respective holding discs, and those upper and lower electrode plates are connected with a high-frequency power supply so that the wafers are respectively etched.
In the plasma treating apparatus disclosed above, the area of the electrode faces of the lower electrode plates is small, if the discs which hold the lower electrode plates are made of an electrical insulating material, so that the area ratio is accordingly large. This possibly allows that apparatus to solve the problem that the power supply capacity is excessively augmented. However, this power plasma treating apparatus does not have a recognition that uniformity of treatments among the respective treated faces of the plural samples to be simultaneously treated is to be improved by equalizing the plasma energies to be applied to the respective treated faces of the samples, but merely monitors the ending point of the treatment of each sample.